The present invention relates to an apparatus and a method for grinding the periphery of an eyeglass lens to fit into an eyeglass frame.
An eyeglass lens grinding machine is known and this machine grinds a lens on the basis of the frame configuration data obtained by tracing (profiling) an eyeglass frame with a tracer. The machine has lens grinding abrasive wheels which are driven with a motor to rotate at high speed and a carriage which clamps the lens between rotating shafts and holds it rotatably. With the lens being revolved, the carriage is rotationally moved on the basis of the frame configuration data such that the distance between the axis of the lens rotating shaft and that of the abrasive wheel rotating shaft is adjusted to permit the grinding of the edge of the lens as it is brought in contact with the abrasive wheel. During the grinding operation, the carriage is rotationally moved such that the grinding pressure on the abrasive wheel is maintained constant by a spring force or the like whereas the required grinding load is exerted between the lens and the abrasive wheel by the rotation of both. The force to rotate the abrasive wheel is transmitted from the associated motor via a belt.
A problem with the conventional eyeglass lens grinding machine is that if with a view to enhancing the grinding efficiency, a high-performance abrasive wheel having great cutting power is employed or a higher rotational speed is adopted, the rotational load increases so much that the abrasive wheel will occasionally stop revolving. If the abrasive wheel stops rotating, an abnormal electric current will flow through the motor to increase the chance of the occurrence of thermal damage or other troubles. In addition, the increased rotational load has often affected the precision of lens processing. To deal with this situation, it has been necessary to perform the intended operation with the rotational speeds of the lens and the abrasive wheel being appropriately set by taking into account the highest grinding load that will be exerted during the processing operation; however, this eventually results in a failure to utilize the potential grinding capabilities of the above-described approaches to the fullest extent.